Cathode mount and lead-in structure for electron tubes



May 25, 1965 A. s. woLFsoN CATHODE MOUNT AND LEAD-IN STRUCTURE FORELECTRON TUBES 2 Sheets-Sheet 1 Original Filed Sept. l0, 1958 ANTHONY S.WOLFSON INV EN l OR.

ATTORNEY May 25, 1965 A. s. woLFsoN 3,185,881

CATHODE MOUNT AND LEAD-IN STRUCTURE FOR ELECTRON TUBES 2 Sheets-Sheet 2Original Filed Sept. l0, 1958 ANTHONY S. WOLF-'SON INVENTOR.

MFM

ATTORNEY United States Patent O l 3,185,881 CATHODE MOUNT AND LEAD-INSTRUCTURE FOR ELECTRON TUBES Anthony S. Wolfson, Sunnyvale, Calif.,assignor to Eitel- McCullough, Inc., San Carlos, Calif., a corporationof California 1 Continuation of application Ser. No. 760,205, Sept. 10,1958. This application July 27, 1961, Ser. No. 127,401 17 Claims. (Cl.313-82) This application is a continuation of application Serial No.760,205 led September l0, 1958.

This invention relates generally to an electron gun and moreparticularly to .an electron gun for use in beam tubes of the type whichdeliver relatively high output power.

In tubes of this character, the electron gun must deliver an electronbeam having a high electron current. A cathode having a large emittingsurface is dictated. In general, larger cathodes include indirectlyheated emitting surfaces. With larger emitting surfaces, to provide moreelectrons, satisfactory support of the heater elements becomesincreasingly dicult.

As higher power electron gunsare constructed, the cooling problem areincreased. If forced air or liquid cooling is employed, the liquid orgas employed must come in heat transfer contact with a large portion ofthe electron gun surface area to provide adequate cooling.

A further problem encountered in high power electron guns is one ofarranging the parts so that a relatively high voltage may be appliedbetween the elements without the occurrence of arcs between theelements.

' It is a general object of the present invention to provide an improvedelectron gun.

It is another object of the present invention to provide an electron gunwhich can be efficiently cooled.

It is another object of the present invention to provide an electron gunin which the complete assembly is carried on a metal base.

It is another object of the present invention to provide an electron gunwhich includes an improved heater assembly.

It is another object of the present invention to provide an electron gunwhich can be operated with relatively high voltages between theelements.

These and other objects of the invention will become more clearlyapparent from the following description when taken in conjunction withthe accompanying drawing.

Referring to the drawing:

FIGURE 1 is an elevational View, partly in section, of the lower part ofa beam tube including an electron gun in accordance with the invention;

FIGURE 2 is a vertical half-sectional View showing an electron gun inaccordance with the invention; y

FIGURE 3 is a bottom view of the electron gun of FIGURE 2;

FIGURE 4 is a plan view of the heater, looking down into the cathodeassembly with the cathode disk removed; and

FIGURE 5 is a view taken along the line 5-5 of FIG- URE 2.

Generally, a beam tube comprises an elongated envelope having anelectron gun at one end of the envelope and a collector electrode at theother end. An electron beam is generated by the gun and passes through adrift tube which extends axially of the tube between the gun and thecollector. In FIGURE 1, the gun portion 11 of a beam tube isillustrated. The end of the Patented May 25, 1965 ICC drift tube whichalso serves as the main anode of the gun 11 is shown at 12.

The electrony gun 11 illustrated includes an oxide coated cathode dish13 which may be prepared for emission in a well known manner. Thecathode dish 13 is indirectly heated by a lamentary heater 16 to bepresently described in detail. A cylindrical focus electrode 17surrounds the cathode dish 13 and shapes the electron beam. A modulatinganode 18 serves to control the current in the electron beam and the mainanode 12 serves to accommodate the beam whereby it is projected aX1allyof the drift tube to the collector (not shown).

The cathode-heater assembly is carried on a metal base plate 19. Thus,the cathode dish 13 is mounted 1n the upper end of a cylindrical cathodesupport 21 which has its lower end secured to the base plate 19 by thescrews 22. A mounting member 23 secured to the base plate 19 receivesthe screws 22. A second cylindrical support 24 is mounted concentricallywithin the support 21 by means of the screws 22 and mounting member 23.The support 24 carries a plurality of heat shields designated generallyby the reference numeral 26. The cylinder also carries at its upper enda cylindrical member 27 which surrounds the lilamentary heater 16. Thus,it is seen that the combination of the heat shields 26 and cylindricalmembers 21 and 27 form a double walled oven-like enclosure which withthe lower surface of the dish 13 Vencloses the lamentary heater 16.Cylindrical members 21, 24 .and 27 are made of thin metal to reduce theconduction of heat from such enclosures to the base plate 19.

The ilamentary heater 16 may be a four-section heater, as illustratedparticularly in FIGURE 4. Each of the sections is supported at its twoends by posts which extend upwardly from the base plate 19. Thus, fourcentral posts 31, are provided, one of which engages the inner end ofeach heater section 32 and four outer posts 33, are provided, one ofwhich engages the outer end. Each of the sections comprises an elongatedfilament bent into a zig-zag shape having straight portions 28 and bightportions 29. The straight portions increase in length to formsector-shaped sections. As `shown in FIGURES 2 and 5, thecentral posts31 are in direct electrical contact with the base plate 19. A pair ofthe outside posts 33 is supported on a ring 36, while another pair ofoutside posts is supported on an axially spaced ring 37. The rings 36and 37 aresupported on and are insulated one from the other, and fromthe base plate 19 by the insulating spacer sleeves 38 associatedwith'the screws 39. Leads 40 and 41 (FIGURE 5) are secured to the rings36 and 37, respectively. These leads are also connected to thelead-through posts 42 and 43, respectively. It is seen that the innerends of the `heater sections 32 are shorted together by means of ametallic ring 30-which is carried by central posts 31. Thus, thesections 32 may be connected so that two ofthe sections are electricallyin parallel with the other two sections or so `that all four sectionsare in parallel with each other to thereby accommodate different voltagesources for a given amount of heating.

The various sections 32 of the heater lament are fitted together likethe pieces of a pie so that a circular heater structure is formedcorresponding in size to cathode dish 13 and the emitting surface isuniformly heated. The 'zig-zag configuration of the lament provides lowheater inductance. As shown, the heater may rbe dished to conform to theshape of the rear surface The base plate 19 also carries ceramiccylinders 46 and 47. The ceramic cylinders are preferably of highrefractory material such as alumina and are metallized at both ends bysuitable metallizing procedures such as by molybdenum manganese powdersintering.

The lower end of the cylinder 46 is suitably sealed to the base plate 19by a sealing assembly designated generally by the reference numeral 4S.The sealing assembly includes a metal ring 49 which has one end suitablybrazed to the base 19, and its other end extending upwardly. A secondring 51 has one end brazed to the ceramic cylinder 46, and its other endsuitably heliarc welded to the other end of ring 49. A ceramic backingring 52 is provided to add strength to the seal.

A lead-in ring 53 provides means for supporting and making electricalconnection to the focusing electrode 17. The ring 53 is suitably brazedbetween the ceramic cylinders 46 and 47. The inner periphery of the ringS3 serves to support the focusing electrode 17, previously described.The electrode 17 may be attached thereto by means of spaced screws 54,for example.

The upper end of the ceramic cylinder 47 carries the modulating anode18. A terminal ring 55 for making connection to the anode is providedand includes seal assemblies S6 and 5'7. The seal assembly 56 includes asealing ring S which is brazed to the upper end of the cylindricalenvelope portion 47 and has its other end suitably heliarc welded to thesealing ring 59. The ring 59 is suitably sealed to the terminal ring 5S,and backing ring 60 serves to strengthen the seal. The assembly 57 issimilar to the one just described in that it includes sealing rings 61and 62 with the sealing ring 61 having one end secured to the terminalring S5, and its other end heliarc welded to the ring 62. The other endof the ring 62 is suitably brazed to the ceramic cylinder 63 whichextends upwardly and supports the main anode 12. A ceramic backing ring64 is provided, but as shown best in FlG- URE 2, an auxiliary ceramicbacking ring 64' is interposed between backing ring 64 and terminal ring55, so that the ceramic backing rings abut each other, and each abuts anassociated envelope section.

The modulating anode 18 is suitably brazed to the ring 55. The anode isconstructed with a rounded recessed portion 66 adjacent to the upper endof focusing electrode 17 The upper end of the focusing electrode 17 isrounded as shown at 67. The opposed surfaces of the anode and focusingelectrode present rounded curved surfaces to one another to reduce thelikelihood of arcing.

The base plate 19 carries mounting lugs '71 which may be brazed thereto.Lead-through terminals, previously referred to, are provided for makingelectrical connection to the posts 33 previously described. Theseconnections may be of the type indicated in FIGURE 2 which include alead-through post 42. Sealing rings 76 and 77 have one end sandwichedbetween and brazed to the ceramic ring 7 8 and the ceramic backing rings49 and 3l., respectively. The other end of the ring '76 is suitablysecured to the base plate 19, as for example, by brazing. The other endof the ring 77 is suitably secured to a flange 82 on the post 42, as forexample, by brazing. Thus a vacuum-tight lead-through is provided.

The outer surface of the electron gun is relatively smooth to providefor intimate contact with a cooling medium. The bottom surface whichsupports the cathode may be efciently cooled by oil or by directing airover the same. The filamentary heater is enclosed within an oven-likeenclosure and is a multi-section heater to provide low heater inductionand even heating of the cathode surface whereby large heaters may beprovided for relatively large cathode dishes. Improved heater supv portis provided and the gun is adapted for high voltage a cathode assemblyincluding an indirectly heated cathode dish supported on said baseplate, a pair of ceramic cylinders carried by said base plate, afocusing electrode supported on said base plate and surrounding saidcathode, an anode carried by the upper end of the upper cylinder, and aplurality of heater sections positioned adjacent said dish, each of saidsections being sector-shaped to uniformly radiate the entire dish.

2. An electron gun comprising a metallic base plate, a cathode assemblysupported on said base plate, said assembly including a dish-shapedemitter, a plurality of heater sections comprising elongated ilamentarymaterial zig-zagged to have straight portions and bight portions withthe straight portions increasing in length to form a sector-shapedsection, said plurality .of heater sections being mounted to cooperatewith one another to uniformly radiate the entire emitter, a pair ofstacked ceramic cylinders carried by said base, a focusing electrodecarried by said base plate and surrounding the upper portion of saidcathode assembly, and an anode carried adjacent the upper end of theupper cylinder.

3. An electron gun comprising a metallic base plate, a cathode assemblysupported on said base, said assembly including a dish-shaped emitter, aplurality of heater sections mounted to indirectly heat said emitter,each of said sections comprising elongated iilamentary materialzigzagged to form straight portions and bight portions with the straightportions having lengths such that a sectorshaped section is dened, saidplurality of sections being mounted to cooperate with one another touniformly radiate the entire emitter, a pair of ceramic cylinderscarried by said base, a focusing electrode carried by said base plateand surrounding the upper portion of said cathode assembly, and anapertured anode carried adjacent the upper end of the upper ceramiccylinder, said anode including an annular recessed portion surroundingsaid aperture and facing an upper rounded end of the focusing electrode.

4. An electron gun comprising a flat metallic base plate, a cathodeassembly supported on said base, said assembly including an indirectlyheated dish-shaped emitter surface and a plurality of heater sectionsdisposed to heat said emitter, each of said sections being sector-shapedwhereby they may be mounted in cooperative relationship to uniformlyradiate the entire emitter, a pair of stacked ceramic cylinders carriedby said base, a focusing electrode carried by said base plate andsurrounding the upper portion of said cathode assembly, and an aperturedanode carried adjacent the upper end of the upper ceramic cylinder, saidanode including an annular recessed portion surrounding said apertureand facing the upper end of the focusing electrode.

5. An Ielectron gun comprising a metal ibase, a cylindrical cathodesupport mounted on said base and extending upwardly, a dish-shapedcathode emitter carried by the upper end of the support cylinder, aplurality of iilament sections mounted to indirectly heat the underneathsurface of the emitter, each of said heater sections comprisingelongated lilamentary material formed to have straight portions andbight portions with the straight portions increasing in length to form asector-shaped filament section whereby the plurality of sections may bemounted in cooperative relationship to uniformly radiate the entireunder surface of the emitter, inner filament sup- |port posts directlymounted on said lbase and extending upwardly to engage one end of theilamentary material forming a lament sec-tion, outer -iilament supportposts mounted on the base and extending upwardly, each serving to engagethe other end of the lamentary material forming a filament section, aninner cylinderextend-ing upwardly and concentric with the emittersupport cylinder, a plurality of radiation shields carried yby saidinner cylinder near the upper end of the same Vand serving to form anoven-like enclosure surrounding `said heater sections, a pair of spacedceramic cylinders mounted on said base and extending upwardly, acylindrical focusing electrode carried by said lbase plate andsurrounding the cathode, and anode supported adjacent the upper end ofthe upper ceramic cylinder.`

6. An indirectly heated cathode assembly comprising a dish-shapedcathode emitter, a plurality of heater sections mounted to indirectlyheat the emitter dish, each of the sections of said heater comprisingelongated filamentary material formed to have straight portions andbight portions Iwith said straight portions having different lengths toform sector-shaped filament sections whereby the sections may be mountedin cooperative relationship to uniformly heat the entire under surfaceof the emitter dish.

7. An indirectly heated cathode assembly comprising a metal base, adish-shaped cathode emitter, a plurality of heater sections mounted toindirectly heat the emitter dish, each of said sections comprisingelongated material -formed to have straight por-tions and bight portionswith said straight portions increasing in length to form sectorshapedfilament sections whereby the sections may be mounted in cooperativerelationship to uniformly radiate the ent-ire surface of the emitterdish, inner heater support post-s directly mounted on said base andextending upwardly, each of said posts serving to engage one end of thelamentary material of each 4filament; section, and a plurality of outerheater support posts mounted on the base and insulated therefrom andextending upwardly, each of said posts lserving to engage the other endof the filamentary Amaterial forming a heater section.

`8. An indirectly heated cathode comprising a metal base, a cylindricalcathode support mounted on said base and extending upwardly, adish-shaped cathode emitter carried by the upper end of the supportcylinder, a plurality of filament sections mounted to indirectly heatthe underneath surface of the emitter, each of said heater sectionscomprising elongated filamentary material formed to have straightportions and bight portions with the straight portionsy having lengthssuch that a sector-shaped filament section is formed whereby theplurality of sections may be mounted in cooperative relationship touniformly radiate the entire under surface of the emitter, innerfilament support posts directly mounted on said base and extendingupwardly to engage one end of the filamentary material forming afilament section, outer filament support posts mounted on the base andextendmg upwardly, each serving to engage the other end of thefilamentary material lforming a filament section, an innercylinderextending upwardly and concentric with the emitter supportcylinder, and a plurality of radiation shields carried by said innercylinder near the upper end of the same and serving to form `anoven-like enclosure surrounding said heater sections.

9. An indirectly heated cathode assembly comprising a metal base, adish-shaped cathode emitter, a plurality of sector-shaped heatersections mounted to indirectly heat the emitterrdish, said sectionsbeing adapted to be mounted in cooperative relationship to uniformlyradiate the entire lower surface of the emitter dish, inner heatersupport posts directly mounted on said base and extending upwardly, eachof saidk posts serving to engage one end of one of the heater sections,a plurality of outer heater posts mounted on the base extending upwardlyand insulated therefrom, each of said posts serving to engage the otherend of one of the heater sections, at least one leadthrough connectionfor making electrical connection through .the base to selected ones ofthe outer heater posts, said lead-through including a conductivelead-through post extending through an enlarged opening Iformed in themetal base, and a metal-ceramic sealing assembly serving to support thelead-through post on the base and insulated therefrom.

10. In an electron tube having an evacuated envelope,

a seal assembly hermetically interconnecting two relatively movableadjacent envelope sections, said seal assembly comprising a metallicsealing yring structure having a first portion hermetioally united toone of said envelope sections, a second portion hermetically united tothe other adjacent envelope sec-tion, and at least two mutually abuttingbacking ring members of dielectric material interposed between saidenvelope sections.

11. The combination according to claim 10, in which said iirst portionof the seal ring structure includes an annular flange having oneperipheral edge portion hermetically united to the associated envelopesection, said second portion of the seal ring structure includes anannular flange having one peripheral edge portion hermetically united tothe other associated envelope section, and said backing ring members areinterposed between the annular flange united to one of said envelopesections and the other adjacent envelope section.

l2. The combination according to claim 10, in which said first portionof the seal ring structure includes a cylindrical fiange radially spacedfrom the associated envelope section, and said second portion of theseal ring structure includes a cylindrical flange hermetically united tothe lcylindrical flange of the first portion of the seal ring structure.

13. In an electron tube having `an evacuated envelope, -a metallicenvelope wall member and a ceramic envelope Wall member adjacent eachother, a metallic sealing ring structure forming a hermetically sealedbridge across the ladjacent portions of said envelope -wall members,said sealing ring structure having one end brazed to said metallic wallmember and its other end brazed to said ceramic wall member, and ceramicstructure means positioned in compression between said envelope wallmembers to form a ceramic-to-ceramic abutment bridged across by saidsealing ring structure.

14. A vacuum tight lead-through assembly comprising an apertured metalplate, a metal electrical conductor extending through said aperture andhaving a radial fiange thereon spaced lfrom one side of said plate,dielectric ring means surrounding said conductor kand extending fromsaid plate to said flange to support compressive loads therebetween, afirst metal sealing ring bonded at one end to said plate and at itsother end to said dielectric ring means, and a second metal sealing ringbonded at one end to said flange and at its other end to said dielectricring means at a location on `the ring means spaced from said other endof the first metal ring, each of said fi-r-st and second metal ringshaving a free flexure portion intermediate its bonded ends.

15. A vacuum tight lead-through assembly comprising an apertured metalplate, a metal electrical conductor extending through said aperture andhaving a radial tiange thereon spaced .from one side of said plate, afirst dielectric ring surrounding said conductor, a first metal sealingring bonded at one end to said plate and at its other end to the endsurface at one end of said first dielectric ring,

a second metal sealing ring bonded at one end to said flange and at itsother end to the end surface at the other end of said first dielectricring, each of said first and second metal rings having a free flexureportion intermediate its bonded ends, and two additional dielectricrings aligned with said first dielectric ring and positioned on oppositesides thereof in contact respectively with the end portions of saidfirst and secondmetal rings which are bonded to the ends of the rstdielectric ring, said additional dielectric rings being also in abutmentrespectively with said plate and said flange.

l6. The combination according .to claim l5 in which said first -metalsealing rings surrounds the outer periphery of one of said additionaldielectric rings and said second metal sealing ringfsurrounds the outerperiphery of the other of said additional dielectric rings.

17. The `combination according to claim 15 in which said additionaldielectric rings are bonded respectively to y PI d the end portions ofsaid first and second metal rings on he side of said end portionsopposite the side on which said end portions are bonded to said firstdielectric ring.

References Cited by the Examiner UNITED STATES PATENTS 2,147,418 2/39Bahls 174-5056 GEORGE N. WESTBY, Prmay Examiner.

RALPH G. NLSON, Examiner.

1. AN ELECTRON GUN COMPRISING A FLAT METALLIC BASE PLATE, A CATHODEASSEMBLY INCLUDING AN INDIRECTLY HEATED CATHODE DISH SUPPORTED ON SAIDBASE PLATE, A PAIR OF CERAMIC CYLINDERS CARRIED BY SAID BASE PLATE, AFOCUSING ELECTRODE SUPPORTED ON SAID BASE PLATE AND SURROUNDING SAIDCATHODE, AN ANODE CARRIED BY THE UPPER END OF THE UPPER CYLINDER,